Hats off to the team; they've been working on the PHP interpreter for just
over a year, and I'm quite impressed by the progress they've made.

While Project Zero is a commercial product, our PHP team has been
making use of the test cases provided by the
qa.php.net community,
thanks to the generous license of the tests.
I'm proud that the team has been able to contribute test cases back to the community as well.
Rob tells me they've contributed more than 1000 tests so far.
They've been using the existing PHP test cases to validate
the interpreter, and have been contributing tests back as they find
undocumented or untested behavior, that we need to implement,
for which we need to determine the exact semantics.

phpBB is just the start; the team has been busy working on getting another
interesting, non-trivial PHP application running. But they told me to keep my big yap shut, so
you'll need to wait a bit longer to find out which one ...